linux-kernel - Re: [PATCH PTI v3 03/10] x86/pti/64: Fix ESPFIX64 user mapping

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Message-ID: <CALCETrV-w-v8bNTE6q5EZwxm=H3HvwY+SDW3jJ3x5DFq3NzkfA@mail.gmail.com>
Date:   Wed, 13 Dec 2017 09:01:50 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH PTI v3 03/10] x86/pti/64: Fix ESPFIX64 user mapping

On Wed, Dec 13, 2017 at 5:12 AM, Kirill A. Shutemov
<kirill@...temov.name> wrote:
> On Tue, Dec 12, 2017 at 07:56:38AM -0800, Andy Lutomirski wrote:
>> The ESPFIX64 user mapping belongs in pti.c just like all the other
>> user mappings.  Move it there and make it work correctly while we're
>> at it.
>>
>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>
> BTW, why do we open-code p?d_alloc() in pti_user_pagetable_walk_*()?
> It seems unnecessary and potentially bogus: see smp_wmb() in __p?d_alloc()
> helpers.

The helpers won't work -- we're allocating kernel-owned tables in the
usermode part of init_mm.  The p?d_alloc() helpers allocate
user-accounted tables in the kernelmode part of the mm.

--Andy